During heavy exercise, when our muscles are working vigorously, they require a lot of energy. To provide this energy, our body undergoes a process called glycolysis, where glucose is broken down through a series of chemical reactions. This process produces lactic acid as a byproduct.
When the level of lactic acid in our muscles increases, it can cause a sensation of cramping. This is because lactic acid is a product of anaerobic metabolism, which occurs when the body is not able to supply enough oxygen to the muscles during intense exercise.
Carbon dioxide (option 1) is produced as a waste product during cellular respiration, not during exercise.
Alcohol (option 3) is not directly related to muscle cramps during exercise.
Water (option 4) is essential for hydration and maintaining bodily functions, but it is not responsible for muscle cramps during exercise.
Therefore, the correct answer is option 2: lactic acid.